NPT- National Pipe Thread Taper- ANSI B1.20.1
NPT pipe threads - dimensions according ANSI/ASME B1.20.1
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Common American National Standard Pipe Taper Threads
- NPT - National Pipe Thread Taper
- FPT - female (internal) National Pipe Taper threads
- MPT - male (external) National Pipe Taper threads
- NPTF - Dryseal American National Standard Taper Pipe Thread (ANSI B1.20.3)
For NPT threads a sealant compound or Teflon tape must be used for a leak-free seal. For NPTF no sealant is needed for a sealing.
Characteristics of NPT (also known as ANSI/ASME B1.20.1 Pipe Threads, General Purpose):
- tapered thread 1o 47'
- truncation of roots and crests are flat
- 60o thread angle
- pitch is measured in threads per inch
Note! Pipe sizes do not refer to any physical dimensions. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. A 3/4" NPT pipe thread has an outside diameter - OD - of 1.050 inches.
Each thread size has a defined number of threads per inch - TPI, or pitch. The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because more than one size have the same TPI.
| NPT - American Standard Pipe Thread Taper 1) | |||
| Pipe Size (inches) |
Threads per Inch TPI - pitch |
Nominal Outside Pipe Diameter OD (inches) |
Tap Drill (inches) |
| 1/16" | 27 | 0.313 | |
| 1/8" | 27 | 0.405 | R |
| 1/4" | 18 | 0.540 | 7/16 |
| 3/8" | 18 | 0.675 | 37/64 |
| 1/2" | 14 | 0.840 | 23/32 |
| 3/4" | 14 | 1.050 | 59/64 |
| 1" | 11-1/2 | 1.315 | 1-5/32 |
| 1-1/4" | 11-1/2 | 1.660 | 1-1/2 |
| 1-1/2" | 11-1/2 | 1.900 | 1-47/64 |
| 2" | 11-1/2 | 2.375 | 2-7/32 |
| 2-1/2" | 8 | 2.875 | 2-5/8 |
| 3" | 8 | 3.500 | 3-1/4 |
| 3-1/2" | 8 | 4.000 | 3-3/4 |
| 4" | 8 | 4.500 | 4-1/4 |
| 4 1/2" | 8 | 5.000 | 4-3/4 |
| 5" | 8 | 5.563 | 5-9/32 |
| 6" | 8 | 6.625 | 6-11/32 |
| 8" | 8 | 8.625 | |
| 10" | 8 | 10.750 | |
| 12" | 8 | 12.750 | |
| 14" | 8 | 14.000 | |
| 16" | 8 | 16.000 | |
1) The taper is 1/16 inch in an inch, which is the same as 3/4 inch in a foot (angle 1o 47')
NPT threads are not interchangeable with NPS - National Pipe Straight - threads.
NPT threads may look similar to ISO 7/1 threads. However, ISO and NPT threads should not be mixed. ISO threads have 55o taper angle versus 60o for NPT. The NPT root and crest configurations are also different from ISO. For ISO threads pitch is usually measured in millimeters (may be expressed in Inch). The pitch are different.
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Related Topics
- Dimensions - Sizes and dimensions of pipes and tubes, and their fittings - inside and outside diameter, weight and more
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